1. Field of the Invention
The present invention relates to an image forming apparatus that uses at least one cartridge and forms images on recording media in an electrophotographic method.
2. Description of the Related Art
Conventionally, there have been image forming apparatuses that form an image by transferring toner images in a plurality of colors from photosensitive drums to an intermediate transfer belt individually in sequence, and then transferring the combined toner image on the intermediate transfer belt to a recording medium. In such apparatuses, any misalignment of a toner image transferred from a photosensitive drum to an intermediate transfer belt from a predetermined position may lead to color misregistration, resulting in poor image quality. In addition, any difference in toner density between the colors on the intermediate transfer belt may cause difference in hue as well as color misregistration, which also results in poor image quality. Accordingly, a detection unit configured to detect the position and density of each toner image on the intermediate transfer belt is located opposite the intermediate transfer belt.
Japanese Patent Application Laid-Open No. 2001-194853 discusses a detection unit and the detection of toner images. The detection unit is disposed opposite a roller where the intermediate transfer belt is stretched around so that a detection defect is not caused due to sagging and flapping of the intermediate transfer belt, and the detection unit detects toner images on the part of an intermediate transfer belt that is wound around the roller.
Japanese Patent Application Laid-Open No. 2007-121983 discusses attachment and detachment of cartridges to and from an image forming apparatus, each of the cartridges having a photosensitive drum. The attachment and detachment are respectively achieved by supporting the cartridges by a plurality of pullout trays and pulling out the pullout trays along the direction in which an intermediate transfer belt is stretched.
FIG. 6 illustrates a conventional image forming apparatus 101 that includes a detection unit 261 configured to detect toner images and toner densities on an intermediate transfer belt 131. The intermediate transfer belt 131 is stretched via rollers 151 and 141 in the direction where photosensitive drums 1 are arranged (direction L). A secondary transfer roller 221 is located opposite the roller 141. The image forming apparatus further includes a pullout tray 341 that supports cartridges CRG. The cartridges CRG are pulled out in the direction L with the pullout tray 341 to be removed from the main body of the image forming apparatus. The detection unit 261 is located opposite the roller 151 across the intermediate transfer belt 131, and is disposed outside of the space S where the cartridges CRG pass to be attached to and detached from the apparatus.
As described above, the conventional image forming apparatus separately includes a space for attachment and detachment of cartridges and a space for a detection unit, which preclude downsizing of the image forming apparatus.